Radio transmitting system



April 21, l931 D. G. 1T|| E RADIO TRANSMITTING SYSTEM Filed Aug. l1,1927 ATTRNEY Patented pr. 21, 1931 l u PATENT OFFICE .noNALn of. Lrr'rLE, or nnenwoon', PENNSYLVANIA, AssIGNoR To WEs'rrNGfHoUsnV Ynrnernrea MANUrnorUnrNer commits, A coaronArroN ori-PENNSYLVANIA y .mimorRANsMrrrING SYSTEM i v- Application filed August 11,.-1927. Serial No.212,153.

i My invention'relates to radio transmitting systems, and it hasparticular relation to` systems in `v'vhich `transmission is effectedbyV utilizing carrier-currents of extremely high -l, frequencies of theorder of 3,000 kilocycles or higher. K f

It has been quite denitely established that less energy is required forcommunication over long distances if high frequencies are used, than isrequired for low frequencies. It is not. feasible, however, in the caseof commercial transmitting stations, to reduce the power to the pointwhereV fadin-g, static, etc., tend to interfere with the messages beingsent, and all of such stations must of necessity-make use of a pluralityof highpower, water-cooled tubes in order that an adequate amount ofenergy shall beradiated.

By reason of the large size of the electrodes in high-power,water-cooled amplifying tubes, their inter-electrode capacity isl high,and when a plurality of them are connected in parallel, as is customaryif large power-output is imperative, the total capacitance is so greatthat it is substantially impossible to'tune the output circuitassociated therewith toV Wave-lengths below 100,1neters. The amount ofenergy radiated at high fre'- quencies therefore, has been limited bythe Y number of power-tubes that could be connectedgin parallel withoutle-tuning theL output circuit from the desired transmission frequency,the most powerful short-wave'transmitter withwhich I was acquaintedprevious to the present invention `being capable of radiating onlyl'kilowattsat 20 meters, and having an effective commercial range ofonly- 500 miles.` j c v Y It is accordingly an Vob] ect of my "invention40 to provide a radio transmitting system that is capable of radiating 4a larger amount of power at high frequenciesv than lsimilar systemsknown to theprior art. f* *l Another object of my invention is 'toprowhich high-power, water-cooled tubes may be successfully utilized. ,i4

Another object of my invention isto .provde a lnovel .circuitI networkfor, a radio *.50 1 transmitting'j system, whereby the effectgof vide a4short-wavetransmitting system in the inter-electrode capacity oftherequisite number of high-power water-cooled amplifying tubes isminimized.

1I attain the aforementioned objects by sub- Vdividing into a pluralityof groups the poweramplifying tubes necessary to provide the requisiteamount of radiated power, and vby so limiting' the number of tubes ineach parallel-connected group that the total inter-electrode capacitythereof is less than the capacity necessary to tune the output circuitvto the `desired frequency., Each group of power-amplifying tubesv hasitsl output circuit coupled to a radiating structure in series-aidingrelation, and is energized from a masteroscillator common to all thegroups, through an individual intermediate amplifier. Y I have alsofound it feasible to utilize a single intermediate amplifier for two ormore groups of powerlamplifiers, and to 4control all of the intermediateamplifiers lfrom another amplifier of lower' power which is directlyenergized froml the master oscillator.

. Among vthe novel features of'my invention are..those particularlysetforth in the appended claims. The ,invention itself, however, bothfas to its organization and its method of operation, together withfurtherobjects and advantages thereof, will best be understood from aconsideration of the following description of a specific embodiment,taken in connection with the accompanying drawing. Y

The single figure ofthe drawing is andiswitches, etc., thathave nobearingon the invention, being omitted for sake ofclarity.

Referring specifically to the drawing, a master oscillator l, which maycomprise a piezo-electric crystal-controlled thermionic device or otherappropriate oscillation generator, is connected in parallel byconductors 2, 3, l' and 5 to a plurality of intermediate amplifiers 6,7v and 8.- Each of 'the intermediate amplifiers may comprise a pluralityof low-power thermionic devices coupled t0- gether 1n "cascade, eitherby'transformers,

resistor-condenser networks or impedances untuned or tuned to thefrequency generated by the master oscillator.

The intermediate amplifier 6 is connected to a second intermediateamplifier 10, the output of which is applied to the input circuit of a.plurality of high-power water-cooled thermionic devices 11, 12, 13 and14 connected in parallel. A. radio frequency transformer 15 may beutilized for coupling thev second intermediate amplifier 10 to the poweramplifier stage as illustrated, or an impedance coupling device of anywell known type may be used if desirable. For examples of couplingdevices, reference may be mace to the patent to Curtis, 1,648,811.

The anodes of the power amplifier thermionie devices 11, 12, 13 and 1liare connected in parallelby a conductor 16 to a tunable output ortank-circuit comprising an inductor 17 and a variable condenser 18. Theinductor 17 is coupled to an inductor 2O included in a radiatingstructure which may comprise an antenna 21 and ground connection 22, orthe ground ccnnection may be replaced by a counterpoise. In the lattercase, the inductor 2O in the antenna circuit need not be in inductiverelation to the output inductor 17, a single lead conductively connectedtherebetween sufiicing to transfer energy from the output circuit to theantenna.

The anodcs of the power amplifier the 1mionic devices are supplied froma source of high voltage (not shown), and the cathodes thereof may besupplied from the saine source (not shown) Vthat supplies the cathodesof the thermionic devices Vcomprised in the intermediate amplifiers andthe master oscillator.

The intermediate amplifier 7 is coupled to an intermediate amplifier 23which may comprise a plurality of thermionic devices of slightly higherpower, though not of the water-cooled type, and the output circuit ofthe intermediate amplifier 23 is coupled to the common input'circuit ofa plurality of highpower water-cooled thermionie devices 2l. 25, 26 and27 connected in parallel. rEhe anodes of the thermionic devices 211, 25,26 and 27 are connected in parallel by a conductor 2S to a tunableoutput circuit comprising an inductor 3() shuntedby a variable condenser31. The inductor 30 is coupled to a second inductor 32 seriallycomprised in the radiating structure. The anodes of the devices 24, 25,26 and 2T, are supplied from theY same high-potential source thatsupplies the anodes for the first described group of power amplifiers.

The intermediate amplifier 8 is coupled to an amplifier 33 of slightlyhigher power, having an output circuitwhich in turn is coupled to thecommon input ci\.uit of a plurality of high-power water-cooled tubes 34,35, 36 'and 37, the corresponding elements of which 'are connected inparallel. Thepower tubes 341,

35, 36 and 37 are connected by a conductor 38 to an individual outputcircuit comprising an inductor 40 shunted by a tuning condenser 41, andthe inductor is coupled to an inductor 12 comprised in the radiatingstructure. The third group of power tubes is supplied with anodepotential from the common source which supplies the first and secondmentioned groups.

In addition to the elements thus far described, a complete radiotransmitting station would comprise modulating devices, additionalpotential sources, various switching and control devices, and numerousother circuit connections which have been omitted from the drawing inorder that applicants invention shall not be needlessly obscured. Theomission of these elements detracts in no way from the completeness ofthe present disclosure.

In the operation of a radio system arranged according to my invention,the intermediate frequency amplifiers which control the several groupsof power amplifiers are energized exactly in phase by the masteroscillator, which is so arranged that the frequency supplied therefromis the same frequency to which the output circuits of the several groupsare tuned. Accordingly, the power amplifiers transmit energy to theradiating structure at a definite predetermined frequency and exactly inphase.

The number of power amplifier tubes included in each group is governedby the platefilament capacity of the individual tubes. Theplate-filament paths of the several tubes in each group are connected inshunt to the output-circuit timing condenser and the total capacitythereof must not be greater than the total capacity required to tune theoutput circuit to the predetermined frequency. Such capacity is largelydetermined by the inductance necessary in order that the couplingbetween the output circuit and the antenna shall be suflicient to insurean eflicicnt transfer of energy therebetween. In other words, it is notfeasible to reduce the inductance of the output inductor below a certaindefinite value for each and every transmission frequency,

and consequently, the maximum value of the timing condenser associatedtherewith is rather sharply determined.

Assuming, for example, in the system illustrated, that it is desired totransmit on a wave length of 100 meters, corresponding to a frequencyyof 3,000 lrilocycles, and that a vpower output of kilowatts isnecessary to satisfactorily cover the desired ytransmission range, itmay bev determined by calculations familia-r to those skilled in theart, that a cerdefinite number of high-power watercooled tubes isnecessary. The number chosen for purposes of illustration, namely 12,Vis `merely an arbitrary number and vbears no relation to the actualnumber required in the ice hypothetical case. If these 12 tubes wereconnected in parallel to a single output circuit having the requiredamount of inductance,

' the total plate-filament capacity would be so much greater than thecapacity necessary to tune such output circuit that it wouldbeimpossible to transmit on the frequency desired, namely 10,0 meters.By distributing the-power tubes in groups as shown, however, the totalcapacity of any one group may be made much less than the required tuningcapacity and cach output or tank circuit may accordingly be accuratelytuned by thevariablecon- -densers shown. v

The total amount of powery transferredv from the several groups ofamplifiers tothe radiating structure is substantially the same when thesystem is arranged accordingpto my invention as when all of the tubesareconnected in parallel to a singlet output circuit, the losses in the twoadditional tuning condensers, in the output inductors and the losses inthe connecting wiring, being substantially negligible.

It is also feasible to further sub-divide the power-amplifiers, ifdesirable, and to energize two or more of the groups from a singleintermediate amplier. In such event, all of the intermediate ampliersmay in turn be energized in parallel from a single intermediateamplifier coupled directly to a master oscillator.

Various other systems of sub-dividing the apparatus between the poweramplifier groups and the master oscillator may be employed, all fallingwithin the scope of my invention, which is mainly directed tothe Ysubdivision of the power-amplifiers proper, into separate groups ofparallel-connected devices, in order that the total inter-electrodecapacity of the devices in any one group shall not prevent propertuningV of an output circuit energized thereby. l

My invention is particularly advantageous,

when it is desired to radiate a relatively large amount of power atfrequencies above 3,000

kilocycles. I haveestablished, by experiment, that when thepower'ampliflers are sub-divided properly, a transmitting system can beprovided which will radiate many times more power than' systems known tothe prior art, wherein all of the power amplifier tubes were connectedin parallel. Although described in connection with space-radio, myinvention is not to be restricted thereto,'but is equally applicable toshort-wave type wherein it is desired to trans- Y v mit a larger poweroutput at higher radio frequency than is normally feasible with all thepower amplifying devices in parallel con Vnectionto a single outputcircuit, a plurality of groups of power-amplifying thermionic n dev icesconnected in parallel, means for applying varying potentials in phaseacross the input-circuits of the groups, a tuned out- Vput circuitforeach group, the said output circuits being coupled to a single workcircuit, the total inter-electrode capacity'of the thermionic devices ineach Vgroup being of such value as to permit the output circuitindividual theretoV to be tuned to high frequencies of the order ofthree thousand kilocycles.

In testimony whereof, I have hereunto subscribed my name this 3rd day ofAugust,

' l.DONALD e. LITTLE.

roo

carrier-current transmission over wires when- Y ever the transmissionfrequency is so high that tube capacity must be taken into account inthe tuning of the output circuit, or in` other situations where largepower-output at i high frequency is necessary.

Although I have shown anddescribed aV single specific embodiment of myinvention,

4 numerous modificationsthereof will be ,ap-

